Biological specimens are often collected for analysis of the levels and concentrations of various analytes contained therein. Although many diagnostics are carried out on biological specimens in their native state, many times the biological specimen must be separated into its constituent components for a variety of reasons. Separating a biological specimen into different constituent parts can maximize the precision, accuracy, and reproducibility of detecting and quantifying analytes of interest within the biological specimen. For example, it is often necessary to filter out solid components from whole blood (e.g., white blood cells, red blood cells, etc.), separate blood serum from whole blood, and separate blood plasma from whole blood, to improve not only the recovery of select analytes from the biological specimen (e.g. viruses, plasma proteins, cytokines, chemokines, immunglobins, etc.) but also improve the subsequent detection and analysis of those analytes. As one example, red blood cells (erythrocytes) scatter and absorb light and, therefore, can adversely affect diagnostic tests that rely on measurements of either reflected or transmitted light. Removing red blood cells can help obtain the most accurate reading possible.
Traditionally, liquid biological specimens have been separated by centrifugation. For example, blood plasma and serum have been separated from whole blood by centrifuging either before (for plasma) or after (for serum) clotting. However, centrifugation requires electricity and expensive equipment that may not be readily available in a clinical laboratory or out in the field. Further, centrifugation can damage analytes of interest (e.g. nucleic acids such as DNA and RNA).
A number of techniques have been devised to avoid this problem. The techniques generally utilize a filtering device that separates a liquid biological specimen into various components. However, these devices have proven to be unsuitable for a variety of reasons. Therefore, what are needed are improved devices and methods that permit efficient and selective separation of liquid biological specimens into at least two constituent components to facilitate subsequent quantitative and qualitative analysis on at least one analyte of interest in at least one of the components.